Process for producing dibasic acids



Dec. 22, 1959 J. A. PATTERSON ETAL 2,918,487

` PRocEss FoP` PRoDucING DIBAsIc ACIDS 2 Sheets-SheetI 1v Filed Sept. 20. 1956 Dec. 22, 1959 J. A. PATTERSON ETAL PROCESS FOR PRODUCING DIBASIC ACIDS Filed Sept. 20. 19,56

Tzara.

2A Sheets-Sheet 2 United States Patent F PROCESS FORPRODUCING DIBASIC ACIDS John A. Patterson, Fishkill, and Stanley M. Pier, Wappingers Falls, N.Y., assignors to Texaco Inc., a cor,

poration of Delaware Application September 20, 1956, Serial No. 611,013

6 claims. (ci. 26o- 452) This invention relates to a process for production of dibasic acids, and more particularly to a process for their production from paraffin wax.

The dibasic acids and their derivatives, e.g., succinic, glutaric, adipic, pimelic, and higher are useful in the manufacture of oil additives, plastics, plasticizers and synthetic lubricants. Esters of the higher molecular weight dibasic acids (C6-H are particularly valuable as synthetic lubricants because of their low pour point and high viscosity index. The dibasic acids and their anhydrides are useful to manufacture alkyd resins with polyhydric alcohols. The acids may be converted also in conventional manner to amides, metal soaps and the like,

Broadly, our process for production of dibasic acids comprises forming a reaction mixture containing Wax oxidate, the product of oxidizing macrocrystalline paraffin wax with a gas containing elemental oxygen, e.g., air, oxygen, and oxygen-enriched air, in the presence of a metalliferous catalyst to a saponiiication number of at least 200, and nitric acid; intensively agitating the reaction mixture and maintaining temperature thereof between 180 and 450 F. for at least one minute, thereby further oxidizing the wax oxidate; and recovering dibasic acids from the resulting mixture comprising further oxidized wax oxidate.

.This two-stage process is rapid and efcient for obtaining good dibasic acid yields consistently and economically However, it is of paramount importance that the air oxidation be carried on to obtain the aforesaid high saponication number, i.e. at least 200, advantageously 300 to 600, and preferably between 450 and 600, before the nitric acid oxidation step. Saponication number is determined by the procedure set forth in ASTM Method of Test D9452T. By this control not only are very high yields of dibasic acids obtained, but also the excellent utilization of nitric acid is achieved and purification processing is simplified, perhaps due to the stripping out of light ends such as low molecular weight monobasic acids, etc., by extensive gas oxidation prior to thetnitric acid treatment.

The macrocrystalline paraffin wax charge for the initial molecular oxygen oxidation (preparatory to the nitric acid treatment) is predominantly a straight-chain sub` stance having from about 20 to 32 carbon atoms per molecule. We have found that quite high yields of dibasic acids can be obtained commencing with a semirefined parain wax containing as little as.0.5% or less oil, a crude scale wax containing somewhat under oil, or a wax concentrate such as is termed a slack wax in the trade.

The primary oxidation is conducted in the presence of a metalliferous catalyst and can be done in any conventional rnanner permitting attainment of the necessary high saponication number. Suitable oxidation of slack waxes for use in our process can be done according to the procedure described in the copending patent application of George B. Kirkwood and Edward F. Tweig, Serial No.` 499,937, ledApril 7, 1955, and entitled Process y 2,918,487 Patented Dec. 22, .1959.

for Producing Oil-Insoluble Materials, now U.S. Patent No. 2,847,439. The less oily waxes, such as a deoiled parain wax obtained by solvent dewaxing a distillate oil, pressing and sweating a distillate oil, or a combination process of extractive solvent refining, can be oxidized to the needed high saponication number with an oxygencontaining gas according to the process disclosed in the patent application of John K. McKinley, Serial No. 192,- 381, filed October 26, 1950, and now abandoned, and entitled Process for Producing High Acid Content Wax Oxidate.

Highly oxidized wax oxidates produced from parailin wax containing less than 5% oil by use of the latter process to obtain neutralization number to saponification number ratios to above about 0.6 are the preferred oxidate charge stocks for use in our invention. In "suchy operations the deoiled paraflin wax is reacted with air in the presence of a metalliferous catalyst at temperature between about 230 to 360 F. and pressure of 30 to 300 p.s.i.g., employing an air feed rate of about 10 to 50 cubic feet per hour per pound of paraffin wax charged,

vnitric acid strength can be from an approximatelyi5% by weight in aqueous solution to virtually nitric acid. Within this broad range there are two specific ranges of acid strength which can be used to special ad- `vantage, each range having specific advantage which will be discussed hereinafter.

In the high strength nitric acid oxidation the nitric acid concentration is advantageously from `about 60 weight percent in aqueous solution to 100% nitric acid, and is preferably about 70% in aqueous solution. From 0.3 to 1 part by weight, generally about 0.66 nitric acid (measured as 100% nitric acid)` per part of the paraffin wax oxidate is charged` as feed to the high strength nitric acid oxidation embodiment of our process. The pressure used s approximately atmospheric to prevent explosions, and the temperature used is advantageously between about and 240 F., preferably between about 200 and 220 F. To main- `tain this temperature rangeit is necessary to cool the reaction mixture; the strong nitric acid is ordinarily added to the wax oxidate at a rate slow enough to keep temperature from going above the control range. To get the best nitric acid utilization in any case it is necessary to agitate the reaction mixture vigorously, preferably with mechanical agitation. Reaction time to get the optimum dibasic yield should be at least a minute and need not be over 10 minutes.

The nitric acid oxidation can be run batch-wise or `continuously, advantageously by incremently (continuously or at intervals) adding `the wax oxidate and nitric acid to a large agitated and cooled body of reaction mixture maintained as a heat dissipatingmedium wherefrom product mixture is withdrawn also incrementally to keep the volume of the reaction mixture essentially constant. Relalate.

hazardous and more difficult to control temperature-wise.

In the low strength nitric acid oxidation the nitric acid used is advantageously broadly between 5 and 40% by Weight aqueous nitric acid, and preferably between and The temperatureof the operation can be maintained between 250 and 400 FL, preferably about 300 y F., with ease. The reaction is operated at pressure beyvater. It can be separated into two distinct liquid phases,

alower' phase containingmost of the water and dibasic ,acids (which phase we have termed an aqueous phase for convenience) and a supernatent phase containing unreacted paraffin, various lipophilic substances, some high- ,er molecular Weight dibasic acids, esters and the like l( whichphase we have termed the oily-phase for convenience). While simple gravity separation is preferred in this step of our process, accelerated separation by .means of a centrifuge or the like is also possible. The oily phase is preferably recycled for reuse to either the nitric acid. oxidation step, or to an air oxidation step as yhereinbefore described preparatory to the nitric acid oxidation step.` Before such recycling the oily phase can be extracted with Water, nitric acid, or an organic solvent such as ethyl alcohol or acetic acid torecover an addivtional, quantity of dibasic acids. The extract solution containing' such` recovered dibasic acids can be blended -thereafter with the previously separated aqueous phase or be processed separately. Alternatively, the entire reaction product can be .mixed with a halogenated solvent such as chloroform before separating the aqueous phase.

In general, we preferto concentrate the separated aqueous phase by distillation before attempting to make ultimate recovery of dibasic acids. This is particularly advantageous when the nitric acid oxidation is conducted with weak acid. The aqueous fraction is fractionally distilled at reduced pressure, preferably about 300 mm. Hg absolute, and vapors comprising Water and lower molecular'weight mono-basic acids are taken as a distil- Some of the nitric acid can also be distilled off, e.g., as a `nitric acid-water azeotrope, but it is preferred to arrest concentration when the nitric acid-water azeotrope boiling temperature is indicated at the still head.

Alternatively, prior to concentration by distillation or evaporation, we have found it advantageous to extract the separated aqueous phase with a higher alkanol of 41-to 18 carbon atoms, e.g., n-butanol, 2ethylhexanol, and nedecanol, and preferably isooctanol, the alkanol being usedy in about 1 to 4 volumes per volume of the aqueous layer. Byso doing, we have found that a major portion of thehigher molecular weight dibasic acids (C6-H are effectively removed from the aqueous mixture along with -a little' nitric acid. The extract solution so formed can `then be heated directly to obtain alkyl esters of the dibasic acids because the small amount of nitric acid in the extract solution acts as a catalyst for the esterification.

fEsters of the higher molecular weight dibasic acids have the greatest utility for use in synthetic lubricants.

Recovery of concentrated dibasic acids is done most conveniently by crystallizng them out of the high boiling concentrate of the aqueous phase obtained from the previously-described fractional distillation. The still pot vresidue from such distillation is cooled to approximately 0` F., although higher and lower temperatures from about 40to about -40` F. can also be used. A magma of `mixed dibasic acid crystals is obtained and filtered. The f ltrate, a mixtureI ofv dibasic acids and concentrated nitric 4 acid, can be recycled to the nitric acid oxidation reactor because the dibasic acids therein are reasonably stable toward further oxidation. Alternatively, the filtrate can be concentrated by redistillation and additional dibasic acids recovered from the resulting concentrate by rccrystallization. This procedure can be repeated as many times as desired for recovery of additional dibasic acid values, not over four times being the general practice.

The mixed dibasic acid crystals can be purified by distillation,sublimation, or treating with a variety of solvent-solid adsorbent systems such as by redissolving in acetone, ethyl acetate, water or chloroform, contacting the solution with activated charcoal, silica gel, adsorptive clay or the like, separating the solid, and recrystallizing. Concentrates preponderating in specific dibasic acids can be made by column partition chromatography, e.g. by placing the mixed acids in aqueous solution on a column of moist silicagel and washing through the chloroformbutanol mixtures containing increasing proportions of the alcohol, the acids being eluted in reverse order to their molecular weight; or by the method described in U.S. Patent 2,716,133 utilizing fractional crystallization from halogenated solvents such as dichlorobenzenes.

Weight proportion of specific dibasic acids in the crystal mixture obtained from crystallizing the aqueous still bottom concentrate is approximately as follows: 5 to 10% C8 and higher, 5 to 15% pimelic (C7), 15 to 25% adipic (C6), 15 to 30% glutaric (C5), and 30 to succinic (C4).

A particular aspect of our invention is the removal or otherwise inactivation of metalliferous residue in the wax oxidate obtained by oxidizing parafin wax with a gas containing elemental oxygen. We have found that a higher yield of the higher molecular weight (C6-H dibasic acids is obtained from nitric acid oxidation of a wax oxidate wherein the metalliferous residue of the catalyst used in the preceding gas oxidation has been substantially completely removed or otherwise sequestered. This is important because the higher molecular weight dibasic acids have the aforementioned special utility for synthetic lubricants and the like. Thus the wax oxidate which has `filtered, or treated with a cation exchange resin such as Amberlite IR-120 (the trade-name for a high density strongly acidic nuclear sulfonic acid cation exchange resin may by Rohm and Haas Company) or Dowex 50 (the `trade-name of a similar strongly acidic cation exchange resin made by the Dow Chemical Company). Suitable cation exchangers are described, for example in U.S. Patent 2,736,741 of February 28, 1956.

In some cases a simple Washing with water or a cold dilute solution of a mineral acid, e.g. nitric acid, is sufcient to remove metalliferous residue. In othercases metalliferous residue can be precipitated with a reagent `such as 8-hydroxyquinoline and filtered from Wax oxidatey in petroleum naphtha solution (e.g. mixed hexanes) or effectively sequestered by Washing with a dilute aqueous solution of a sodium polyphosphate or sodium hexametaphosphate, and discarding the aqueous extract. Certain chelating agents are also useful for such extraction, e.g. ethylenediamine tetraacetic acid andother amino acids of this nature.

The common metalliferous catalysts used in air oxidation are compounds of polyvalent metals such as naphthenates,stearates, metal salts of organic acids, or previously oxidized wax fractions, and the like. Compounds of manganese, chromium, vanadium, calcium, zinc, lead, titanium, mercury, and cerium are among the useful catalysts. In the air oxidation of parain wax potassium permanganate is thepreferred catalyst, and it is employed in amounts ranging from 0.1 to 1% of the total wax charged, preferably about 0.4% dispersed in the wax as a water solution (which distributes the permanganate very uniformly during the air oxidation). Alternatively, oxides Ato the drawings.

such as managanese dioxide, zinc oxide, and the like can be used.

Our process can be more fully understood by referring In Figure 1 molten paraffin wax is charged to lirst stage oxidation reactor through line 11. Such wax is typically obtained by solvent dewaxing a paraHin-base distillate. Metalliferous catalyst such as an aqueous solution of potassium permanganate is also charged to reactor 10 through line 12, and air is introduced through line 13. The reaction mixture is heated rapidly to temperature of about 340 F. and then maintained in the control range by indirect heat transfer with submerged coils of heat exchange fluid. After 3 to 12 hours there is obtained a wax oxidate having saponication number above 200, generally approaching 500. This oxidate is withdrawn from vessel 10 by line 15.

At this stage the oxidate can be sent directly to a` nitric Vacid oxidation in vessel 20 or, optionally and preferably,

fed to vessel 16 and then filtered. Metalliferous residue is Withdrawn from the system through line 18. ln lieu of such filtration, it is also possible to use sequestration, ion exchange removal, or chelation, or precipitation of metalliferous residue.

The so-treated wax oxidate is then passed through line 19 into second stage oxidation reactor 2l) wherein it is vigorously agitated with nitric acid at temperature between 180 and 4509 F., the pressure and temperature being regulated in accordance with the nitric acid strength as hereinbefore discussed. By-product gases, e.g., carbon dioxide, nitrogen, nitrogen dioxide, and nitrous oxide, are vented from line 22. Nitrous gases of nitric oxide or nitrogen in a higher stage of oxidation can be recovered and converted to additional nitric acid in conventional fashion. The average residence time of the reaction mixrture in `vessel 20 should be at least one minute and need not be longer than l0 minutes.

The further oxidized wax oxidate is then withdrawn through line 23 and passed into gravity separator 24 (e.g.

a tank) wherein a lower aqueous liquid phase and a supernatent oily liquid phase form. The oily phase is withdrawn from line 26 and can be recycled to the iirst `stage oxidation vessel 10 by means of line 28, or to the second stage oxidation vessel by means of line 27. Gptionally, the oily phase before recycle is passed through line 29 into extractor 30 wherein it is extracted with water or a light organic solvent such as methyl alcohol entering line 31. The oily ralinate is then withdrawn through line 32 and passed into line 27 and/or 28. The aqueous extract phase is withdrawn from extractor 3i) by means of line 33 and adrnixed with the aqueous phase passing from separator 24 to concentrator 34 by means of line 25.

Concentration of the aqueous phase takes place in apparatus 34, e.g. a batch fractional distlling apparatus comprising a kettle, distlling column, still head, condenser, and auxiliary lines and controls. Low boiling lmaterials such as water, monobasic acids and some nitric acid are withdrawn from the still head in conventional fashion and sent to tankage through lines 35, 36, and 37, respectively. When the nitric acid-water azeotrope boiling temperature occurs at the still head in the reduced pressure distillation, concentration is arrested and the still bottoms are passed through line 38 into crystallizer 39. Herein the still bottoms are cooled to about 0 F. Optionally, before cooling, nitric acid traces can be removed by treatment of the still bottoms with a weakly basic ion exchange resin, e.g. the kind described in U.S. Patent 2,689,832; alternatively, much or all of the nitric acid traces can be precipitated with organic bases, e.g. quinaldine, ortho or meta toluidine, Nitron (the trade-name for l,4-diphenyl3,5endo andino-4,5-

dihydrol,2,4triazole), or the like, and the still bo-ttoms filtered. After cooling there results a slurry of crystalline dibasic acids in mother liquor. This is passed through line 40 into separator 41, e.g., a filter. Mother liquor is Withdrawn from line 42 and can be further concentrated,

recrystallized, and separated for retained dibasic acid values. However, the mother liquor is preferably recycled to vessel 20 for reprocessing along with fresh wax oxidate. Mixed dibasic acids are withdrawn from separator 41 by means of line 43 and may be further purified by distillation, sublimation, or recrystallization from solvents, optionally after having been treated with a solid absorbent such as activated charcoal.

A further embodiment of our process includes withdrawing at least a portion of the aqueous phase from separator 24 through lines 25 and 47 into extractor 48. Herein a higher alkanol such as isooctanol is admitted through line 44, thoroughly contacted with the aqueous material, and separated into a raffinate phase, which is withdrawn through line 45, and an extract solution phase, which is withdrawn through line 46. The oily raffinate can be recycled to vessels 10 and/or 20 for reprocessing along with fresh oxidizable material. The extract solution, containing alkanol, dibasic acids, and a small amount of nitric acid, can be used directly as an esterication reaction mixture in conventional fashion.

Materials of construction for the air oxidation reactor is preferably aluminum or an austenitic stainless steel, but also can be made of other corrosion-resisting materials such as glass-lined steel and the like. Corrosionresistant equipment such as austenitic stainless steel is preferred throughout the rest of the system. Intermittent storage facilities, pumps, valves and other auxiliary equipment have not been shown in the foregoing drawing, but are provided wherever necessary or desirable.

Figure 2 represents a modification of the nitric acid oxidation step to utilize nitric acid values to the greatest extent. In this modiiication air oxidized wax oxidate is passed into second stage oxidation reactor 20 by means of line 19 and reacted as described hereinbefore with nitric acid entering line 21. The further oxidized product is withdrawn through .line 23 and passed into gravity separator 24 wherein a lower aqueous liquid phase and a supernatent oily liquid phase form. The oily phase is withdrawn from line 26 and can be recycled to lirst stage oxidation vessel 10 or to second stage oxidation vessel 20.

The aqueous phase is withdrawn from: separator 24 by means of line 25 and passed through line 57 into recovery reactor 58, which is fed with a supplementary portion of air oxidized wax oxidate entering line 59. In the recovery reactor residual nitric acid in the aqueous phase is further reacted with the supplemental portion of air oxidized wax oxidate at 250-400" F. and 200-800 p.s.i.g. using intensive agitation. This serves to cut down on and substantially eliminate any excess nitric acid being fed to the dibasic yacid concentration step. The reaction products from the recovery reactor are passed through line 61 into gravity separator 62 wherein a lower aqueous phase and a supernatent oily liquid phase again form. The aqueous phase containing dibasic acids is withdrawn from the separatory by means of line 63 and passed to the concentration step described in connection with Figure 1. The oily liquid phase is withdrawn by means of line 64 and can be sent back `to vessel 20 for further oxidation, or, preferably, passed to another oxidation reactor 65 wherein it is contacted with fresh nitric acid entering line 66 in accordance with the principles of my invention. The reaction products of this operation is passed then by means of line 68 into gravity separator 69. The lower aqueous liquid phase is recycled by means of lines 70 and 57 to the recovery reactor 58, while the supernatent oily phase is passed through line 71 and then joins other oily phase material being withdrawn from line 26 for subsequent recycle use.

The following examples show ways in which our invention has been practiced but are not to be construed as limiting the invention. All parts shown are parts by weight and all percentages are weight percentages except as otherwise specially noted.

Example 1 partsV of a petroleum oxidate fraction, obtained as the naphtha-insoluble (light naphtha having EBP. of 200 F. from a paraffin base crude) portion of an oxidate made by air-blowing a semi-relined 125 to 127 F. melting point macrocrystalline petroleum wax in the presence of a metalliferous catalyst, said oxide fraction having a neutralization number of 198 and a saponilication number of 306, was heated to 86F. 50 parts by weight of concentrated (70%) nitric acid was added in live portions With stirring and the maximum temperature reached was 108 F. After the reaction the entire product was mixed with 75 parts by volume of water. This mixture was extracted twice with parts by volume of ether and separated into a water phase and an ether extract phase. Upon evaporation of the water phase, a crystalline solid was obtained'which was soluble in 20% sodium hydroxide solution and also released carbon dioxide from 10% sodium carbonate solution. A sample of this solid had a neutralization No. of 880 indicating that it was preponderantly of dibasic acid. By evaporation of the ether extract a hard waxy residue was recovered which had a neutralization No. of 418.

Example 2 300 parts of an oxidate, prepared by air blowing a semi-refined 125 to 127 F. melting point macrocrystalline petroleum wax in the presence of a metalliferous catalyst, having a neutralization No. of 324, saponication No. of 473, hydroxyl No. of 11, and containing 6.8% unsaponifiable material, was oxidized with 200 parts by weight of concentrated (70%) nitric acid. The oxidate was heated to about 90 C. (194 F.) and the nitric acid added dropwise during 4 hours at rate to control the temperature between 91 and 97 C. (196- 207" F.). During the run, gases were formed which had the following composition, mol percent: nitrogen plus carbon monoxide, 10; carbon dioxide, 44; nitrous oxide, 19; nitric oxide, 25; and balance, 2. The liquid product 'was extracted with 200 parts by volume of methylpentanes and the aqueous and organic layers separated. Crude dibasic acids were separated from the aqueous phase by distilling until crystallization of the residue started, chilling the distillation residue, filtering off the crystals and then further concentrating the liquid filtrate by distillation. This process was repeated to obtain 3 batches of crystals whose total amount was 139 parts, equivalent to 46.4% of the oxidate charged. The bulk of these crystals (115 parts) obtained in the iirst separation had a neutralization No. of 647. By column partition chromatography this fraction was shown to contain 135.2% succinic acid, 15.7% glutaric acid, 19.1% adipic acid, 9.3% pimelic acid and 19.7% higher dibasic acids. The organic layer was stripped of rnethylpentanes by distillation leaving a waxy residue amounting to 137 parts equivalent to 45.6% of the original oxidate charge.

Example 3 yconcentrated (70%) nitric acid and 765 parts by Volume of water. Stirring was started and the autoclave was heated at 300 F. for 3 hours during which time the pressure rose to 570 lbs. per square inch. The reactor wascooled to room temperature, the resultant gases were bled off through a caustic trap. The liquid product was blended with 100 parts by volume of chloroform and then syphoned from the reactor. The aqueous layer was 'separated and concentrated, cooled, and filtered to isollate dibasic acids. Concentration and filtration were repeated three times to obtain a total yield of 38parts by weight of crude dibasic acids, equivalent tov 76 weight percent of the wax oxidate charged. The organic layer was stripped of chloroform by distillation leaving an oily residue amounting to 9 parts, equivalent to 18% of the oxidate charged, and having a neutralization No. of 354.

Example 4 Crude wax oxidate, prepared by the air oxidation of semi-rened 125 to 127 F. melting point petroleum wax using 0.4 potassium permanganate as catalyst and having a neutralization No. of 311, saponiication No'. of 475, hydroxyl No. of 14, carbonyl No. of 5, iodine No. of 3, 7% unsaponitiable material, and 0.19% ash was ltered at 80 C. to remove 0.9% of insoluble material. By this treatment the ash content was reduced to 0.014%, indicating that substantially all of the metalliferous catalyst residue was removed. 300 parts of the filtered oxidate and 2400 parts of 10% nitric acid were placed in a stainless steel autoclave and stirred and heated at 300 F. for one hour. The pressure developed was 440 lbs. per square inch. The reactor was cooled and the product diluted with 300 parts by volume of chloroform. Upon separation and distillation of the aqueous layer the crude dibasic acids were obtained as the residue. The following acids were present:

Parts Succinic acid 42 Glutaric acid 23.8 Adipic acid 2l Pimelic acid 12.6 Suberic acid 8.4 Azeleic acid 2.8 Higher acids 1.4

Upon distilling off the chloroform from the organic layer a residue amounting to 118 parts, or 39.3% of the oxidate charged, was obtained.

By way of contrast, oxidation using the same procedure on the same wax oxidate except that it was uniiltered and thus contained all metalliferous residue from the air oxidation, the following dibasic acids were obtained:

Parts Succinic acid 42.4 Glutaric acid 23 Adipic acid 17.4 Pimelic acid 10.7 Suberic plus azeleic acid 8.0 Higher acids 0.7

Three runs were made each by charging 150 parts of an oxidate obtained by the air oxidation in the presence of 0.4% potassium permanganate catalyst of a semi-refined to 127 F. melting point petroleum wax, having a neutralization No. of 243, a saponiiication No. of 365, and 12.8% unsaponiiiable material, together with 240 parts by volume of concentrated (70%) nitric acid and 2300 parts by volume of water to a. stainless steel autoclave. The autoclave was heated at 300 F. for three hours with stirring, cooled and vented. The product mixed with parts of chloroform. The dibasic acids isolated from the resulting aqueous solutions amounted to from 69 to 75 parts in the several runs, the average yield of. dibasic acids being 48% based on the oxidate charged. The amounts of chloroform soluble material varied from 53 to 55 parts, or an average of 36% of the oxidate charged.

150 parts of a composite of the chloroform-soluble materials from the above three runs was stripped of chloroform, then using 240 parts by volume of concentrated 70% nitric acid and 2300 parts by volume of water at temperature of 300 F. and autogenous pressure for three hours with stirring. Upon venting the reactor, dissolving the product in chloroform, separating the aqueous and organic layers, and distilling the respective solutions, 41.5 parts of crude, water-soluble dibasic acids, equivalent to 27.7% of the chloroform-soluble material charged or 13.3% of the original oxidate used, and 77 parts of a waxy product equivalent to 51.3% of the charge, was obtained.

Example 6 Parts Glutaric acid 1.3 Adipic acid 3.1 Pmelic acid 4.1 Suberic acid 25.7 Azeleic acid 1.3 Other material 27.5

The water, after ether extraction, was evaporated, leavlng a dark viscous oil which contained the following:

Parts Succinic acid 8.3 Glutaric acid 5.4 Adipic acid 5.8 Pimelic acid 3.3 Suberic and azeleic acids 6.7 7.5

Other material 3 Example 7 100 parts by volume of the aqueous phase from nitric acid oxidation operated in a manner similar to the one described in Example 3, above, said aqueous phase containing 5.53 parts by weight of dibasic acids, was extracted with 25 parts by volume of isooctyl alcohol. 60.4% of the dibasic acids were extracted by the alcohol, and, as shown in the table below, the higher molecular weight acids were concentrated in the alcohol resulting in a solution suitable for esteritication.

Unex- Ex- Isooctyl Weight, tracted tracted Alcohol Percent Aqueous Aqueous Extract, x- Solution, Solution, parts traeted parts parts Total Dibasic Acids 5. 53 2. 19 3. 34 60. 4 Succinic Acid 1.13 0.62 0.51 45.1 Glutarlc Acid 1. 75 0. 705 1. 045 59. 5 Adipio Acld 1. 35 0. 565 0 985 72. 9 Pimelic Acid` 0.74 0.21 0. 53 71. 9 Buberic and Higher Acids.... 0.56 0.09 0.47 83. 9

Example 8 The following table describes the operating conditions of a continuous dibasic acid production unit during 3 periods of 11.42 hours, 11.08 hours, and 8.75 hours, respectively. The wax oxidate, made by air oxidation of parain wax in the presence of metalliferous catalyst, had neutralization No. of 295, saponiiication No. of 474,

2% of unsaponiiiables, API gravity of 1.50, SSU viscosl ity at 210 F. of 113, and 0.47% ash. The wax oxidate and nitric acid were separately preheated and fed into the base of a vertical cylindrical reactor jacketed for temperature control and packed with Berl saddles. The oxidized product was withdrawn near the top of the reactor, cooled, and separated into oily and aqueous fractions.

First Second Third Period Period Period Wax Oxidate Charge Rate, Parts per Hour--- 4. 78 4.81 8. 20 Nitric Acid Charge Rate, Parts per Hour (as HN O3) 4.01 4.00 6. 99 Weight Percent Nitric Acid Concentration.- 10. 7 10. 6 14. 5 Temperatures, F.:

Wax Oxidate to Reactor 312 312 243 Acid to Reactor 319 320 261 Reactor Outlet. 352 352 384 Cooler Outlet 146 146 152 Reactor Pressure, p.s.i.g 222 217 310 Superficial Residence Time, Minutes, based on charge liquid densities at 60 F. and the charge owing through empty reactor in the absence of evolved gas 13. 9 13. 8 10.6 Vent Gas, Parts per Hour 2. 48 2. 35 4. 4 Vent Gas, Composition, Volume Percent:

N2 15 15 9. 9 5.8 49 49 48. 2 15 15. 5 14. 2 21 20. 5 21 0 0 0.2 0 0 0.7 Oily Phase Production, Parts per Hour-. 1. 5 .2. 545 3. 13 Aqueous Phase Production, Parts per Hour-- 37.4 37. 1 47. 3 Overall Recovery, Weight; Percent 99 98. 6 97. 2 Collected Aqueous Phase Analysis:

Total Nitric Acid, Parts 7. 76 7. 33 7. 80 Total Dibasic Acids, Parts 24. 08 20. 98 30.13 Succnic. l0. 40 Glutaric 6. 10 Adipic 5. 38 gilnclic 3. 23

u )eric A7nleic 502 Total Nitric Acid Reactcd, Parts 53. 35 Parts of Dibasic Acids per Part of Wax Oxidate Charged 0.420 Parts of Dibasic Acids per Part of Nitric Acid Consumed 0.633 0. 567 0.565

We claim:

1. A process for production of dibasic acids which comprises oxidizing macrocrystalline parain wax with :a gas containing elemental oxygen in the presence of a :metalliferous catalyst until the resultant reaction mixture has a saponication number between 450 and 600, thereby forming a wax oxidate containing metalliferous residue; substantially completely removing said metallifertous residue from the wax oxidate; further oxidizing said wax oxidate with 60-100% nitric acid at temperature between about 200 and 220 F. and pressure substan tially atmospheric for at least about one minute with intensive agitation; separating the resulting reaction mixture into an aqueous phase and an oily phase; and recovering dibasic acids from said aqueous phase.

2. The process of claim 1 wherein said oily phase is recycled to at least one of the foregoing oxidation steps.

3. A process for production of dibasic acids which ycomprises oxidizing macrocrystalline paraffin wax with a gas containing elemental oxygen in the presence of a metalliferous catalyst until the resulting reaction mixture has saponication number between 300 and 600, thereby :forming a wax oxidate feed containing metalliferous residue; substantially completely removing said metalliferous .residue from the wax oxidate feed; further oxidizing said wax oxidate feed with 5-40% nitric acid at temperature between about 250 and 400 F. and pressure between 200 and 800 p.s.i.g. for at least about one minute with intensive agitation; separating the resulting reaction mixture into an aqueous phase and an oily phase; and recovering dibasic acids from said aqueous` phase.

4. The process of claim 3 wherein said oily phase is recycled to at least one of the foregoing oxidation steps.

5. The process of claim 3 wherein said separated aqueous phase is passed into agitated contact with supple mental wax oxidate feed at temperature between` about 250i and 400 F. and pressure between 200 and 800 p.s.i.g. for at least about one minute, said supplemental wax oxidate feed containing no substantial quantity of metalliferous residue and having been made by oxidation with elemental oxygen; the reaction mixture thus formed is separated into a second aqueous phase and a second oily phase; and dibasic acids are recovered from said second aqueous phase.

6. A process for production of dibasic acids which comprises oxidizing macrocrystalline paraflin wax with a gas containing elemental oxygen in the presence of a metalliferous catalyst until the resulting reaction mixture has a saponiiication number of at least about 200, thereby forming a wax oxidate containing metalliferous residue; 15 2,794,040

ingydibasic acids from the` resulting mixture comprising` further oxidized wax oxidate.

References Cited in the le of this patent UNITED STATES PATENTS 2,723,988 Nelson Nov. l5, 19,55 2,771,482 Brown et al Nov. 20, 1956` 2,779,779 Meyer et al. u Jan. 29, 1957 2,791,598 Brown et al. May 7,. 1957 Annable et al. May 28, 1957 

6. A PROCESS FOR PRODUCTION OF DIBASIC ACIDS WHICH COMPRISES OXIDIZING MACROCRYSTALLINE PARAFFIN WAX WITH A GAS CONTAING ELEMENTAL OXYGEN IN THE PRESENCE OF A METALLIFEROUS CATALYST UNTIL THE RESULTING REACTION MIXTURE HAS A SAPONIFICATION NUMBER OF AT LEAST ABOUT 200, THEREBY FORMING A WAX OXIDATE CONTAINING METALLIFEROUS RESIDUE: SUBSTANTIALLY COMPLETELY REMOVING SAID METALLIFEROUS RESIDUE FROM THE WAX OXIDATE; FURTHER OXIDIZING THE WAX OXIDATE WITH NITRIC ACID AT A TEMPERATURE BETWEEN ABOUT 180* AND 450*F. USING INTENSIVE AGITATION; AND RECOVERING DIBASIC ACIDS FROM THE RESULTING MIXTURE COMPRISING FURTHER OXIDIZED WAX OXIDATE. 